Reversible, also called invertible or lossless, image data hiding can imperceptibly hide data in digital images and can reconstruct the original image without any distortion after the hidden data has been extracted out. Among the various digital image formats, Joint Photographic Experts Group (JPEG) formats are by far used the most often nowadays. Hence, how to reversibly hide data in a JPEG image file is important and useful for many applications including authentication, secure data systems, and covert communications. For example, linking a group of data for some purpose to a cover image in a reversible way is particularly critical for medical images, high accuracy images, images used for legal purpose and other environments in which the original image is of great importance. Furthermore, the invented technology is expected to be able to apply to the I-frame of Motion Picture Experts Group (MPEG) video for various applications mentioned above.
Reversible data hiding by using the histogram shifting techniques has been reported in the literature. Reversible data hiding was first applied to the histogram of an image in the spatial domain in Z. Ni, Y. Q. Shi, N. Ansari, W. Su, “Reversible data hiding,” IEEE International Symposium on Circuits and Systems (ISCAS03), Bangkok, Thailand, May 2003; and A. van Leest, M. van der Veen, and F. Bruekers, “Reversible image watermarking,” Proceedings of IEEE International Conference on Image Processing (ICIP), II-731-4 vol. 3, September 2003. In addition, the technique was applied to the histogram of DCT domain and integer wavelet transform domain. In general, the histogram shifting technique has achieved dramatically improved performance in terms of embedding capacity versus visual quality of stego image measured by peak signal noise ratio (PSNR). However, none of the above-discussed lossless data hiding methods apply to JPEG images.
In fact, there are not many reversible data hiding techniques that have been developed for JPEG images to date. Some background art techniques are reported in J. Fridrich, M. Goljan and R. Du, “Invertible authentication watermarking for JPEG images,” Proceedings of IEEE Information Technology and Computing Conference (ITCC), pp. 223-227, Las Vegas, Nev., USA, April 2001; J. Fridrich, M. Goljan, and R. Du, “Lossless data hiding for all image formats,” Proc. of SPIE, Electronic Imaging 2002, Security and Watermarking of Multimedia Contents IV, vol. 4675, San Jose, Calif., pp. 572-583, 2002; and J. Fridrich, M. Goljan, Q. Chen, and V. Pathak, “Lossless data embedding with file size preservation,” Proc. SPIE Electronic Imaging 2004, Security and Watermarking of Multimedia Contents, San Jose, Calif., January 2004.
In the first two background art references cited above, the least significant bit plane of some selected JPEG mode coefficients is losslessly compressed, thus leaving space for reversible data embedding. Consequently the payload is rather limited. In the third background art reference cited above, the run-length encoded alternating current (AC) coefficients are modified to losslessly embed data into JPEG images, aiming at keeping the size of JPEG file after lossless data hiding remaining unchanged. However, the payload is still rather limited (i.e., the highest payload in various experimental results reported in the third paper is 0.0176 bits per pixel (bpp)).